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Handbook of Size Exclusion Chromatography and Related ...

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Table 1 Factors for GPC Resolution<br />

Factors N=a To increase R Remarks<br />

Column length N, a Longer or<br />

multicolumn<br />

Increased backpressure<br />

Particle size N Smaller Increased backpressure<br />

Internal width <strong>of</strong> column a Wider Reduced backpressure<br />

MW range <strong>of</strong> separation a Narrow but<br />

adequate<br />

Pore volume/solid body a Larger ratio More fragile<br />

Injection volume N Small Less pressure fluctuation<br />

Column temperature N Higher Reduced backpressure<br />

Bubbles may form after<br />

column<br />

Table 2 Number <strong>of</strong> Theoretical Plates at Different Temperatures<br />

Temperature Peak a<br />

1,320 b<br />

BHT 162 c<br />

Room temperature 1,230 19,200 18,300<br />

358C 1,480 19,400 19,300<br />

508C 1,520 21,800 21,000<br />

a Samples were run using one PLGel 100A ˚ column in THF, at 1.0mL/min.<br />

b This sample is polystyrene with MW 1,320, from Polymer Laboratories. This is not a real<br />

monodispersed material; the number <strong>of</strong> theoretical plates is an apparent number.<br />

c This is 1-phenylhexane, the unimer <strong>of</strong> oligostyrene.<br />

1-phenylhexane (the unimer), <strong>and</strong> a low MW oligostyrene at three different<br />

temperatures. All increased roughly by 15% from room temperature to 508C.<br />

3 DETECTOR SENSITIVITIES<br />

Unlike high MW polymers, the SEC detector sensitivity <strong>of</strong> oligomeric material<br />

varies with respect to MW. In the case <strong>of</strong> the most <strong>of</strong>tenly used SEC detector, the<br />

refractive index (RI) detector, the signal is the excess refractive index (Dn) dueto<br />

solute, which can be expressed as:<br />

© 2004 by Marcel Dekker, Inc.<br />

Dn ¼ (n n0) ¼ k dn<br />

c (3)<br />

dc

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